170 



CIRCULATION OF THE BLOOD 



(1) a small elevation, (2) a very steep ascent, (3) a subsequent much slower 

 ascent, or a plateau almost parallel to the abscissa, (4) a rapid fall from the 

 maximum, (5) a very gradual ascent (Fig. 56). 



The maximum pressure of the ventricular systole has been determined also 

 by the Hg-manometer, by interpolating between the heart and the Hg a maxi- 

 mum valve which opens with every increase in the ventricular pressure, but 

 prevents the return of mercury with the fall of pressure. 



The maximum pressure in the left ventricle may amount to 200 mm. Hg. 

 (in the dog). The pressure in the right ventricle is considerably lower; in 

 the dog the pressure in the pulmonary arteries varies between 10 and 33 mm. 



Hg., in the rabbit between 6 and 35, and 

 in the cat between 8 and 25 mm. Hg. 

 A definite ratio between the pressures in the 

 lesser and the greater circulations does not 

 obtain, because even with very great varia- 

 tions in pressure in the greater circulation, 

 only relatively slight variations generally 

 occur in the lesser (cf. Section III, 8). 



On the pressure curves given above, 

 various single points are found which are 

 sometimes more, sometimes less clearly 

 marked. Some of these e. g., various peaks 

 which occur in many tracings at the height 

 of the plateau are doubtless artifacts pro- 

 duced by extreme vibrations, while others 

 are definite expressions of events in the 

 heart. The latter we must discuss, there- 

 fore, somewhat more in detail. 



At the beginning of the pressure curve, 

 before the ascent which corresponds to the 

 strong rise in the ventricular systolic pres- 

 sure, a slight elevation is sometimes very 

 beautifully shown. This elevation, as we 



learn from Fig. 56, is caused by the auricular contraction and the consequent 

 rise in pressure in the ventricle. 



In the intracardial pressure curve of the horse, Chauveau has demon- 

 strated between the peaks corresponding to the auricular systole and the begin- 

 ning of the true ventricular systole a more or less clearly marked inter systole 

 (Fig. 57). A similar elevation appears now and then also in the cardiagram 

 of man, and represents doubtless a brief rise in the pressure inside the ven- 

 tricle. This has been referred with great probability to the elastic rebound 

 of the vei-tricular wall after the completed auricular systole. Obviously it can 

 appear clearly only in case a measurable time intervenes between the maximum 

 of the auricular contraction and the beginning of the ventricular systole. 



After the ventricular systole has begun, it requires a certain time before 

 the power of contraction becomes sufficient to overcome the pressure exerted 

 by the blood in the vessels upon the semilunar valves (period of rising ten- 



FIG. 57. Pressure curves of the right 

 ventricle (V D}, of the left ventricle 

 (V G), and of the aorta (A o) of the 

 horse, after Chauveau. 3-4 au- 

 ricular contraction; 4-2 intersys- 

 tole. To be read from left to right. 



